The present invention relates to a process for the production of an anticoagulant composition, as well as the composition so produced. The present invention further relates to an apparatus containing such composition for use in the sampling of blood and a method of sampling blood.
The analysis of whole blood requires the use of an anticoagulant, typically in the collection apparatus, in order to prevent coagulation of the collected blood sample prior to its analysis. The use of heparin, both in dry and liquid form, is known, as is its ability to bind a certain portion of the electrolyte within the blood sample (e.g. sodium, potassium and/or calcium ions). This electrolyte binding is undesirable since it effectively prohibits an accurate analysis of blood electrolyte concentration, particularly sodium, potassium and calcium ion concentrations. The measurement of calcium ion concentration has recently received increased attention in the field of cardiac medicine in view of the heart""s sensitivity to calcium ion concentration and the recent development of blood gas machines to monitor the concentration thereof.
Various solutions to the problems associated with this electrolyte binding by heparin have been heretofore proposed. For instance, Radiometer A/S of Copenhagen has previously marketed anticoagulant compositions for use in connection with blood sampling apparatus in the form of capillary tubes having a coating on the inner wall of the tube of dry sodium heparinate. These compositions are further said to contain a specified amount of calcium chloride in an effort to compensate for the blood""s calcium anions which will be bound by the heparinate once in solution. The use of this composition therefore does not provide a complete solution to the aforementioned problem since this composition introduces additional sodium and chloride ions into the blood sample, thereby altering an accurate analysis of the concentration of sodium and chloride within the blood sample. Moreover, the added calcium ions represent only a replacement for an approximation of those expected to be bound by the heparin component. Therefore, an analysis for calcium ion concentration within the collected sample while improved, is not rendered totally accurate.
U.S. Pat. No. 4,687,000 (assigned to Radiometer A/S) discloses a method for treating a blood sample with an anticoagulant as well as a blood sampling device. The disclosed method involves contacting a collected blood sample with (a) an anticoagulant capable of binding cation species within the blood and (b) an additive including selected cationic species in the amounts compensating for proportions of these cation species bound by the anticoagulant. The disclosed method still does not represent a true solution to the aforementioned problems, however, since again the cationic species present in the additive represent only estimations of the cations expected to be bound rather than the true and exact amounts.
It is therefore an object of the present invention to provide a process for the production of an anticoagulant composition.
It is further an object of the present invention to provide a method for treating blood with anticoagulant which allows for accurate analysis of the sodium, potassium and calcium ions present therein.
It is further an object of the present invention to provide an apparatus which is both a container for the claimed anticoagulant and useful in the practice of the claimed method.
The present invention comprises a process for the production of an anticoagulant and the anticoagulant produced thereby.
The present invention further is directed to a blood sampling device comprising
(a) a receptacle means defining a blood receiving space therein for receiving a blood sample;
(b) a blood inlet means for introducing a blood sample into the blood receiving space; and
(c) an anticoagulant present within said blood receiving space, said anticoagulant comprising the product of the process of claim 1.
The present invention further comprises a method for collecting blood samples through use of the claimed composition.
As stated above, the present invention relates to a novel anticoagulant composition and the process for its production. The invention further relates to an improved method for the collection of blood samples and an apparatus useful in the practice thereof.
The anticoagulant composition of the present invention is lithium heparinate modified with a heavy metal salt such as zinc acetate. It is produced through a procedure which is outlined below.
A quantity of sodium heparin is obtained is and dissolved in water to a consistency such that it is suitable for passage through a bed of an ion exchange resin. Sodium heparin is from various sources such as beef lungs and/or mucosa, pork mucosa, and whole pork intestines. It is further commercially available from such sources as Viobin Corporation of Waunakee, Wisconsin. Preferably, the solution so formed has a concentration of about 30,000 to about 50,000 u/cc.
The solution is then passed through a column of an acidic ion exchange resin. The resin may comprise any acidic ion exchange resin or mixtures thereof. Such resins include IR-120 (a resin available from Rohm and Haas Company having a matrix structure of divinylbenzene (8%) and a sulfonic acid functionality). Preferred is the IR-120 resin. Especially preferred is the use of the IR-120 resin in the hydrogen form. The effluent from the ion exchange column is collected and monitored for the presence of heparin such as through the use of toluidine blue. The effluent should further possess a pH of 3 or less. The acidity of the effluent can be maintained through adjustment of the residence time of the solution within the ion exchange column.
The acidic heparin effluent is then converted to a heavy metal heparin salt through contact with a heavy metal-containing compound. Conversion to a zinc, barium or copper salt is preferred. These salts include zinc acetate dihydrate as well as the chlorides and sulfates of zinc, barium and copper. Use of zinc acetate dihydrate is preferred. In the case where zinc acetate dihydrate is used, it is added to the acidic effluent in an amount ranging from about 2 to about 7 grams, preferably about 5 grams, per each 15 grams of sodium heparin originally introduced into the ion exchange column. Use of other of the above-named heavy metal containg compound include the use of similar molar amounts. The pH solubility of the solution is further monitored to ensure that the pH is maintained so as not to exceed about 3.
To the heparin-heavy metal salt produced in the preceding step is then added an aqueous solution of lithium salts such as lithium acetate, lithium hydroxide or lithium carbonate such that the resulting solution possesses a pH in the range of about 6 to about 7. The use of lithium hydroxide is preferred. Use of an aqueous 10% lithium hydroxide solution is especially preferred. This solution is agitated, typically for a period of about 4 to about 24 hours, preferably at least 8 hours, to permit for chelation of the lithium and stabilization of the solution""s pH. Additional amounts of either solution may of course be added to correct for pH deviations.
The pH stabilized solution may then be filtered through a filter media suitable to remove any bacterial contamination and/or insoluble matter picked up during prior processing. Use of a media having a pore size of about 0.22 microns is preferred. The filtered solution may then be dried in a suitable apparatus such as a Lyophilizer produced by Hull or Virtis.
Drying times and temperatures should be maintained at a level such that undue degradation of the heparinate composition is avoided. Once dried, the heparin composition should further be preferably stored in an area of low humidity in view of the hydroscopic nature of the material.
The claimed composition is found to possess about 6 to about 8% by weight of zinc through atomic absorption spectroscopy. If heavy metals other than zinc were used, the claimed composition contains equivalent molar amounts of such metals.
The amount of the heparin composition used in conjunction with sampled blood should be sufficient to ensure against coagulation of the blood sample. However, use of great excesses of the composition should also be avoided in order to minimize any potential interference in the analysis of the collected blood sample. It is therefore preferred that use be made of the least amount of the anticoagulant composition which adequately prevents blood sample coagulation. It has been found, for example, that the use of about 8 to about 150 international units (IU) of the composition per milliliter of sampled blood is useful in the practice of the claimed method. Preferably, about 20 to about 80 IU/ml are used. Most preferably, about 50 IU/ml are used. The above quoted ranges for the concentration of anticoagulant adequate to prevent blood coagulation are concentrations which are recognized as useful in collection devices and indeed are present in products which are currently commercially available. These ranges do not however refer to use in Sherwood ABG syringes described herein.
However, it should be noted that lower concentrations of anticoagulant are being increasing used and recommended. For instance, the proposed guidelines issued in September 1992 by the NCCLS subcommittee on Electrolytes (Document C31-P) recommends the use of heparinate in an amount of about 15 IU/ml. Lower concentrations (e.g. below 10 IU/ml) have also been reported as sufficient. Indeed Sherwood Medical ABG syringes currently contains 12 (+/xe2x88x922) IU/ml of heparinate. Use of such lower levels of anticoagulant is within the scope of the present invention.
The claimed anticoagulant composition may be predissolved prior to its being contacted with a collected blood sample or, more preferably, utilized in its dried state wherein it is dissolved upon its contact with the collected blood sample. Most preferably, the composition is present in dried form within the collection apparatus for the blood sample, i.e. capillary tube, syringe or vacuum container. In this way, it is available for immediate contact with the sampled blood as it is collected. The dried form of the claimed composition may be present within the collection apparatus as a free solid (i.e. powder) or as a film or coating present on the walls or other internal structure of the collection apparatus. For instance, the composition may be deposited on or within an inert carrier body, such as disclosed in U.S. Pat. No. 4,687,000, the contents of which are hereby incorporated by reference.